It is known to prepare a coffee drink, in particular espresso coffee, using coffee powder obtained by grinding coffee beans. The coffee drink, hereafter also called simply coffee, is generally obtained by extraction, that is, percolation with boiling water under pressure. In particular, machines are known for the production of espresso coffee, which are provided with a tank for the water from which, using a pump, the water is delivered at high pressure to a heating unit. From this hot water and/or steam is obtained, which is used in a coffee extraction unit, where it is percolated through the coffee powder to produce the espresso coffee.
It is possible to use coffee powder obtained by grinding coffee beans of the same type or variety, or to use a mixture of coffee powder obtained by grinding coffee beans of a different type or variety.
Different proportions of different types or varieties of coffee in the powdered mixture influence the organoleptic properties of the coffee prepared with them, such as taste, aroma, acidity and body.
Real coffee lovers or enthusiasts can detect variations, even minimal, in the organoleptic properties, and these can influence their judgment of the drink and the choice or preference of one coffee powder mixture obtained by grinding a certain selection of beans of different types of coffee compared with another mixture. Furthermore, even a minimum contamination of mixtures of coffee powder formed from different selections of coffee can lead to detectable differences.
Document EP-A-2.710.938 describes a coffee-grinding device provided with grinders to grind coffee beans stored in a container disposed above the grinders. The ground coffee powder is discharged through an exit disposed under the grinders. The coffee-grinding device comprises a fan housed in the container for the un-ground coffee provided above the grinders. The fan is provided to generate a stream of air that flows through the container of ground coffee above the grinders, from an air inlet to an air outlet, so as to remove the essential oils from the un-ground coffee. The stream of air does not pass through the grinders, nor does it interact with the ground coffee. In fact, the essential oils removed from the un-ground coffee are removed both to be recovered for the purpose of producing aromas, and also to prevent the essential oils from dirtying the grinders, and therefore the coffee-grinding device needs fewer cleaning interventions and is more efficient. This known solution therefore does not solve the problem of the contamination between mixtures of coffee powder formed from different selections of coffee ground in sequence in the grinding member.
Document WO-A-2014/206944 describes a coffee-grinding dispenser provided with a support base containing a grinding chamber. The base houses an electric motor with a shaft rotationally connected to a second shaft, but axially free, to rotate a driven grinding wheel. The base also houses a bushing inside which the second shaft rotates freely but is axially constrained. The bushing has a threaded lateral surface that cooperates with a rigid threaded portion with the base. The driven grinding wheel is axially constrained to the bushing. The coffee-grinding dispenser also comprises means to rotate the bushing axially. Furthermore, the base houses a fixed grinding wheel facing the driven grinding wheel inside the grinding chamber, the fixed grinding wheel being non-removably connected in a determinate position to the base frame.
Document WO-A-01/48711 describes an automatic machine for selling products in grains, such as for example coffee beans or other products.
There is therefore a need to perfect a device and method for grinding coffee beans that can overcome at least one of the disadvantages of the state of the art.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.